1. Technical Field
The present invention relates to an ultrasound diagnostic apparatus, and more particularly to a technology of forming a three-dimensional bloodstream image.
2. Related Art
In the medical field, an ultrasound diagnostic apparatus transmits and receives ultrasonic waves to and from a living organism and generates an ultrasound image on the basis of a reception signal obtained by transmission and reception of the ultrasonic waves. Typical ultrasound images may include a two-dimensional tissue image, which is a monochrome image (B-mode image), and a two-dimensional bloodstream image, which is a color image. A two-dimensional bloodstream image is color representation of Doppler components or motion information (e.g., velocity information, power information, and so on) which are contained in a reception signal. A two-dimensional tissue image may be formed by reference to the motion information. In general, a two-dimensional tissue image and a two-dimensional bloodstream image are combined to form a combined image, which is then to be displayed on a display.
In recent years, three-dimensional ultrasound diagnostic apparatuses which form a three-dimensional tissue image by reference to volume data obtained by transmission and reception of ultrasonic waves with respect to a three-dimensional space within a living organism have been in wide-spread use. Conventionally, a three-dimensional tissue image is formed by using a volume rendering method, for example, and is a stereoscopic representation of a tissue (e.g. an organ) within a living organism. Meanwhile, motion volume data can be obtained by extracting motion information from volume data. Here, motion volume data refers to three-dimensional data formed of the motion information. By applying three-dimensional image processing to the motion volume data, a three-dimensional bloodstream image can be formed.
JP 2005-157664 A (Reference 1), JP 2005-40622 A (Reference 2), JP 2006-51202 A (Reference 3), and JP 2001-17428 A (Reference 4) disclose conventional ultrasound diagnostic apparatuses which form a three-dimensional ultrasound image.
The motion volume data generally contain not only bloodstream data for which image formation is desired but also noises (including clutter) and so on for which image formation is not desired. If a rendering processing is directly applied to the motion volume data containing a great amount of noise to form a three-dimensional bloodstream image, sufficient image quality cannot be achieved in such a three-dimensional bloodstream image. While noises similarly appear in a conventional two-dimensional bloodstream image, disadvantages resulting from appearance of noises on a two-dimensional bloodstream image are not very significant, because these noises were present on a scan plane which is a two-dimensional plane. In a three-dimensional bloodstream image, on the other hand, noises which are present over the whole three-dimensional space are imaged. Consequently, if a great amount of noise appears around and in front and back portions of a bloodstream on a three-dimensional bloodstream image, these noises obstruct observation of the bloodstream. Here, the amount of noise within a three-dimensional space is several tens to several hundreds times as much as that present on a two-dimensional plane.